Blood group AB is an example of _ .
Correct answer: C. Co-dominance
- A. Complete dominance
- B. Recessive alleles
- C. Co-dominance
- D. Incomplete dominance
Explanation
Option A describes one allele being completely dominant over the other allele i.e. one allele is dominant while the other is recessive so, in a heterozygous condition, only the dominant allele is expressed as a trait. However, in the AB blood group, BOTH A and B antigens are expressed so, that one allele is not completely dominant over the other. Option B describes alleles that are only expressed in the phenotype in homozygous conditions; they will not be expressed if a dominant allele is present in heterozygous conditions. One allele is recessive over the other, but in this case, both traits are expressed. Option C is the correct answer, as it describes the scenario in which both alleles are equally expressed in the phenotype. Since both antigens are expressed individually, this means that both alleles are equally expressed. Option D describes a scenario in which the alleles are expressed in such a way that the phenotype is actually a mixture of intermediate expression of both alleles. The individual alleles are not expressed completely. For example, alleles of black and white fur color are not expressed as black and white spots, they are expressed as grey fur color, i.e. an intermediate or mixture of the two traits.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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